The ultimate goal in the design of a prosthetic knee joint is the duplication of the action of a human knee joint, both in stationary support and in walking. In the past, knee joints have been provided with a single axis pivot to permit angular motion between the femoral and tibial portions of the prosthetic leg. Knee joints have also been provided with locking mechanisms to provide secure support during prolonged standing, to aid an unstable walker, or to provide stability or uneven ground, stairs, and ramps.
The more difficult problem in prosthetic knee design has been the duplication of the knee motion required for walking or striding. One technique known in the prior art has been the provision of a braking device in the knee mechanism which is actuated by weight applied to the knee. The braking mechanism has usually comprised a brake band extending about a brake drum.
The problem often encountered in using this and other forms of braking apparatus is that the brake does not release immediately upon removal of the weight which causes brake actuation. Thus, during a normal walking stride, when the prosthetic leg reaches the posteriormost position and the weight is shifted to the other leg, the prosthetic knee does not immediately pivot freely as it is moved forward to the anterior position. This deficiency in the prior art mechanisms can only be overcome by a pronounced weight shift to the other leg, resulting in an obvious and characteristic limp.
Such a limp is a great deviation from the ideal goal of duplication of the human knee motion. More importantly, the limp is an embarrassment for many prosthetic knee wearers, and it also represents an increased hazard during walking.